Pacemaker

The pacemaker is an electronic biomedical device that can regulate the
human heartbeat when its natural regulating mechanisms break down. It is a
small box surgically implanted in the chest cavity and has electrodes that
are in direct contact with the heart. First developed in the 1950s, the
pacemaker has undergone various design changes and has found new
applications since its invention. Today, pacemakers are widely used,
implanted in tens of thousands of patients annually.

Background

The heart is composed of four chambers, which make up two pumps. The right
pump receives the blood returning from the body and pumps it to the lungs.
The left pump gets blood from the lungs and pumps it out to the rest of
the body. Each pump is made up of two chambers, an atrium and a ventricle.
The atrium collects the incoming blood. When it contracts, it transfers
the blood to the ventricle. When the ventricle contracts, the blood is
pumped away from the heart.

In a normal functioning heart, the pumping action is synchronized by the
pacemaker region of the heart, or sinoatrial node, which is located in the
right atrium. This is a natural pacemaker that has the ability to create
electrical energy. The electrical impulse is created by the diffusion of
calcium ions, sodium ions, and potassium ions across the membrane of cells
in the pacemaker region. The impulse created by the motion of these ions
is first transferred to the atria, causing them to contract and push blood
into the ventricles. After about 150 milliseconds, the impulse moves to
the ventricles, causing them to contract and pump blood away from the
heart. As the impulse moves away from each chamber of the heart, that
section relaxes.

Unfortunately, the natural pacemaker can malfunction, leading to abnormal
heartbeats. These arrhythmias can be very serious, causing blackouts,
heart attacks, and even death. Electronic pacemakers are designed to
supplement the heart's own natural controls and to regulate the
beating heart when these break down. It is able to do this because it is
equipped with sensors that constantly monitor the patient's heart,
and a battery that sends electricity, when needed, through lead wires to
the heart itself to stimulate the heart to beat.

In addition to outer units, artificial pacemakers can be permanently
implanted in a patient's chest. This is done by first guiding the
lead through a vein and into a chamber of the heart, where the lead is
secured. Fluoroscopic imaging helps facilitate this process. The pacemaker
itself is next placed in a pocket, which is formed by surgery just above
the upper abdominal quadrant. The lead wire is then connected to the
pacemaker, and the pocket is sewn shut. This is a vast improvement over
early methods, which required opening the chest cavity and attaching the
leads directly to the outer surface of the heart.

History

The idea of using an electronic device to provide consistent regulation of
the beating heart was not initially obvious to the early developers of the
pacemaker. The first pacemaker, developed by Paul Zoll in 1952, was a
portable version of a cardiac resuscitator. It had two lead wires that
could be attached
to a belt worn by the patient. It was plugged into the nearest wall
socket and delivered an electric shock that stimulated the heart of a
patient having an attack. This stimulation would usually be enough to
cause the heart to resume its normal function. While moderately effective,
this early pacemaker was primarily used in emergency situations.

Through 1957 and 1960 significant improvements were made to Zoll's
original invention. In an attempt to reduce the amount of voltage needed
to restart the heart and increase the length of time electronic pacing
could be accomplished, C. Walton Lillehei made a pacemaker that had leads
attached directly to the outer wall of the heart. Later, in 1958, a
battery was added as the power source, making the pacemaker truly
portable, which allowed patients to be mobile. This also enabled patients
to use the pacemaker continuously instead of only for emergencies.
Lillehei's pacemaker was external. William Chardack and Wilson
Greatbatch invented the first implantable pacemaker. It was implanted in a
living patient in 1960.

The modern technique for putting a pacemaker into a patient's heart
was developed by Seymour Furman. Instead of cutting open the chest cavity,
he used a method of inserting the leads into a vein and threading them up
into the ventricles. With the leads inside the heart, even lower voltages
were needed to regulate the heartbeat. This increased the length of time a
pacemaker could be inside a person. Although his method was not widely
used initially, by the late 1960s most cardiac specialists had switched to
Furman's endocardial pacemakers. Since then improvements have been
made in their design, including smaller pacemaker devices, longer lasting
batteries, and computer controls.

Raw Materials

The materials used to construct pacemakers must be pharnacologically
inert, nontoxic, sterilizable, and able to function in the environmental
conditions of the body. The various parts of the pacemaker, including the
casing, microelectronics, and the leads, are all made with biocompatible
materials. Typically, the casing is made of titanium or a titanium alloy.
The lead is also made of a metal alloy, but it is insulated by a polymer
such as polyurethane. Only the metal tip of the lead is exposed. The
circuitry is usually made of modified silicon semiconductors.

Design

Many types of pacemakers are available. The North American Society of
Pacing and Electrophysiology (NASPE) has classified them by which heart
chamber is paced, which chamber is sensed, how the pacemaker responds to a
sensed beat, and whether it is programmable. Despite this vast array of
models, all pacemakers are essentially composed of a battery, lead wires,
and circuitry.

The primary function of a pacemaker battery is to store enough energy to
stimulate the heart with a jolt of electricity. Additionally, it also
provides power to the sensors and timing devices. Since these batteries
are implanted into the body, they are designed to meet specific
characteristics. First, they must be able to generate about five volts of
power, a level that is slightly higher than the amount required to
stimulate the heart. Second, they must retain their power over many years.
A minimum time frame is four years. Third, they must have a predictable
life cycle, allowing the doctor to know when a replacement is required.
Finally, they must be able to function when hermetically (airtight)
sealed. Batteries have two metals that form the anode and cathode. These
are the battery components through which charge is transferred. Some
examples include lithium/iodide, cadmium/nickel oxide, and nuclear
batteries.

Pacemaker leads are thin, insulated wires that are designed to carry
electricity between the battery and the heart. Depending on the type of
pacemaker, it will contain either a single lead, for single chamber
pacemakers, or two leads, for dual chamber pacemakers. With the constant
beating of the heart, these wires are chronically flexed and must be
resistant to fracture. There are many styles of leads available, with
primary design differences found at the exposed end. Many of the leads
have a screw-in tip, which helps anchor them to the inner wall of the
heart.

The circuitry is the control center of the pacemaker. Located here are
heart monitoring sensors, voltage regulators, timing circuits,

and externally programmable controls. The circuitry is composed primarily
of resistors, capacitors, diodes, and semiconductors. Modern pacemaker
circuitry is a vast improvement over earlier models. With the application
of semiconductors, circuit boards have become much smaller. They also
require less energy, produce less heat, and are highly reliable.

The Manufacturing
Process

Pacemakers are sophisticated electronic devices. Therefore, some
manufacturers rely on outside suppliers to provide many of the component
parts. The construction of a pacemaker is not a linear process but an
integrated one. Component parts such as the battery, leads, and the
circuitry are constructed individually, then pieced together to form the
final product.

Making the battery

1 The primary type of battery used in pacemakers is a lithium/iodine
cell. One method used by manufacturers to make these batteries involves
first mixing together the iodine and a polymer such as
poly2-vinylpyridine (PVP). They are heated together, forming a molten
charge-transfer complex. This liquid is then poured into a half
moon-shaped, preformed cell which contains the other components of the
battery, including the lithium anode (positive charge) and a cathode
collector screen. The iodine/polymer blend solidifies as it cools to
form the cathode. After the cathode is formed, the battery is
hermetically sealed to prevent moisture from entering.

Making the leads

2 The leads are typically composed of a metal alloy. The wire is made by
an extrusion process in which the metal is heated until it is molten,
then pushed through an appropriately sized opening. It is cut, then
bundled with many other wires and treated with a polymeric insulator
such as polyurethane. One end of the lead wires is fashioned with a
shaped tip, and the other is fitted with a pacemaker connector.

Making the motherboard

3 The motherboard contains all the electrical circuitry of the
pacemaker, including

the semiconductor chips, resistors, capacitors, and other devices.
Using a complex method known as hybridization, these components are
combined to form a single complex circuit. Construction begins with a
small board (less than 0.32 sq in [2 sq cm]) which has the electronic
configuration mapped out. The appropriate components are put in place on
the board. They are then affixed using a minimum number of soldering
welds.

Final assembly and packaging

4 When all of the component pieces are available, final assembly takes
place. The circuitry is connected to the battery, and both are inserted
into the metal casing. The casing used for a pacemaker is typically
formed using titanium or a titanium alloy. It is constructed in multiple
pieces that are sealed together after the other pacemaker components are
introduced. A fitting is also affixed to the casing, providing a
connecting point for the leads.

5 The finished devices are then put into final packaging along with
accessories. After being exhaustively tested, they are then sent out to
distributors and finally to doctors.

Quality Control

The quality of each pacemaker is ensured by making visual and electrical
inspections throughout the entire production process. These tests will
detect most flaws. Since the batteries must be absolutely reliable, they
are specially manufactured and exhaustively tested, thereby increasing the
associated costs tremendously. The functionality of each finished
pacemaker is also tested before it is sent out for sale. Many of these
tests are done under varying environmental conditions, such as excessive
humidity and stress.

Manufacturers set their own quality standards for the pacemakers that they
produce. However, standards and performance recommendations are required
by various medical organizations and governmental agencies. In the United
States, pacemakers are classified as Class III biomedical devices, which
means they require pre-market approval from the United States Food and
Drug Administration (FDA).

The Future

With the increasing numbers of senior citizens in the United States, it is
anticipated
that a greater percentage of the population will require pacemakers. As
research efforts continue, future devices promise to be longer lasting,
more reliable, and more versatile. Advances in battery technology, such as
using radioactive isotopes for power, will undoubtedly improve the
longevity of implanted pacemakers. Developments in microelectronics should
provide even smaller devices which are less prone to environmental
interferences. A late-breaking development in the field is the application
of cardiac pacemaking technology to the brain. In this system, scientists
connect the lead wires to a specific site on the brain and stimulate it as
needed to regulate heartbeat. This device has been shown to be
particularly effective in calming the tremors associated with
Parkinson's disease.

Periodicals

User Contributions:

When people refer to a pacemaker, they are actually discussing a pacing system: a pacemaker, a pacing lead, and programmer. Two parts are placed inside the body.

The pacemaker is a small battery-powered device containing a tiny computer. It is designed to constantly watch your natural heart rate. When needed, it can deliver its own electrical signals to help the heart beat faster or more efficiently. These signals are much like those of a normal heart.

A pacing lead is an insulated wire that carries the tiny electrical pulse to the heart so a heartbeat can begin. One end of each lead connects to the pulse generator. The other end is placed directly in a heart chamber or on the outer surface of the heart.

The third part, the Programmer, is kept in a hospital or clinic. A nurse or doctor uses this specialized computer to see how the pacemaker is working and if necessary, to adjust the settings of a pacemaker.

Where are the device implanted?

A doctor implants each type of device in much the same way. The device itself is typically implanted just under the skin near the shoulder. Cardiac devices send electrical energy to the heart through thin, specially coated wires called leads. Leads are positioned inside or on the surface of the heart.

A pacemaker system can monitor and treat your heart rhythm by delivering electrical energy to pace your heart when it senses a slow rhythm. But it is not for everyone, including patients with certain steroid allergies. Patients who have additional medical conditions that may not allow the pacemaker to function appropriately should not receive a device. Procedure risks include infection, tissue damage and kidney failure. In some cases, the device may not respond to your heart rhythm. In rare cases severe complications or device failures can occur. Electrical or magnetic fields can affect the device. Only your doctor knows what is right for you. This device is available by prescription only. Individual results may vary.

After havinga major heart attack on 08-Apr.-1992; I later had a total of three (3) defiberlaters installed in my l/s tummy & l & r chest area. Two of the devices were replaced due to complications. On 20-may-2004 I rec'd a complete heart transplant at the Cleveland Clinic, Cleveland, Ohio. All of the prior (old) leads were not removed.08-May- 2014!! AICD's were made by Medtronic I thinkDuring the transplant something happened to my back and now I can only walk very short distances or stand a short time. I have geen told that they need to run an MRI test on me but; they (Dr.s) wont do it because they are afraid of the wires being magnetic & afraid that it will harm me. I know I have had an MRI with the leads in me but they cannot find it in my records. PLEASE HELP ME!!! Will it harm me or not? W are the leads made of--and are they magnetic. I will be waiting for your reply

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